Punching tool

Abstract: In a punching tool having a punch body (23), a punch driver (33) integral with the punch body, a punch head (45) disposed over the punch driver and struck by a striker (59), a punch guide (15) for guiding the punch body, a stripper plate (17) disposed under the punch guide, and a stripping spring (51) interposed between the punch guide (15) and the punch driver (33), the punching die further includes a first damping member (39) interposed between the punch guide (15) and the punch driver (33) so as to be elastically deformable within a predetermined deflection value. Owing to the presence of the first damping member (39), it is possible to reduce noise generated when the punch body (23) is returned upward by a strong urging force of the stripping spring (51) after work has been punched, thus preventing overall noise generated during punching processing.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a punching tool, and more specifically to a punching tool which can reduce punching noise generated during punching processing. Description of the Related Art Work mounted on a lower die can be punched by moving an upper tool up and down relative to the lower die. During this punching processing, punching noise is inevitably generated. To reduce the generated punching noise, conventionally a damping member made for example of urethane or the like has been disposed on a stripper plate provided at the lower portion of a punch guide for constituting a part of the upper tool. According to another proposal, the cutting edge of the punch body is formed with a shear angle to reduce the punching noise. In the conventional method of disposing a damping member made for example of urethane or the like on the stripper plate provided at the lower portion of the punch guide, there exists a problem in that the work surface is easily scratched because needle-shaped chips generated during punching processing adhere to the damping member. In addition, the life time of such a damping member is short and in addition it is rather difficult to mount or bond the damping member on the punch guide. On the other hand, in the conventional method of forming the cutting edge of the punch body with a shear angle, it has been difficult to reduce noise down to a sufficiently low level. The publication "Tooling and Production" Vol. 50, No. 7, October 1984, Solon US pages 74-75, suggests the general use of a damping ring for reducing stamping noise and US-A-5 176 057 discloses a punching tool as recited in the preamble of claim 1, in which there is a collision between the flange region of the punch guide and the driver end. SUMMARY OF THE INVENTION The primary object of the present invention is to provide a punching tool as recited in the preamble of claim 1 which can reduce the noise generated by collision of a punch guide with the lower portion of a punch driver, whenever a punch body is returned by an urging force of a stripping spring after the work has been punched. The above-mentioned object is achieved by the combination of the technical features of claim 1. Further, it is preferable that the punching tool further comprises a second elastically deformable damping member (47) interposed between the punch driver (33) and the punch head (45). Further, it is preferable that a cutting edge of the punch body (23) is formed with a shear angle (25). Further, it is preferable that a driver end (31) fixed to a lower portion of the punch driver (33), and said first damping member (39) is interposed between the punch guide (15) and the driver end (31) laterally protruding with respect to the punch driver (33) and surrounding the lower portion of said punch driver. Since, in the punching tool according to the present invention, the first damping member (39) is interposed between the punch guide (15) and the punch driver (33) and is elastically deformable within a predetermined degree of deformation, it is possible to reduce noise generated due to collision of the punch driver with the punch guide, whenever the punch body is returned upward by a strong urging force of the stripping spring after the work has been punched. Further, since the second damping member is additionally interposed between the upper surface of the punch driver and the lower surface of the punch head and further since the punch body is formed with a shear angle, it is possible to reduce the overall noise generated when work is punched. BRIEF DESCRIPTION OF THE DRAWINGS Fig.1 is a cross-sectional view showing an embodiment of the punching tool according to the present invention, when applied to a turret punch press; Fig.2 is an enlarged cross-sectional view showing the same punching tool, when seen from an arrow 200 shown in Fig.1; Fig.3 is an enlarged, partially cross-sectional, perspective view showing the same punching tool, when seen from an arrow 300 shown in Fig.1; Figs.4 to 10 are cross-sectional views for assistance in explaining the noise generating sequence of the punching tool according to the present invention; and Fig.11 is a graphical representation showing the measured noise levels of the respective elements of the punching tool, which are generated during the punching processing. DETAILED DESCRIPTION OF THE EMBODIMENTS An embodiment of the punching tool according to the present invention will be described hereinbelow with reference to the attached drawings. In Fig. 1, a turret punch press 1 (as an example of a punch press) is provided with an upper turret (an upper tool holder) 3 and a lower turret (a lower die holder) 5. The upper turret 3 is formed with a plurality of turret holes 7 at regular angular intervals along the circumference thereof. Further, an upper tool 11 is fitted into each turret hole 7, respectively. Similarly, the lower turret 5 is formed with a plurality of turret holes 9 at regular angular intervals along the circumference thereof. Further, a lower die 13 is fitted into each turret hole 9, respectively. Fig. 1 shows a punching tool structure in which only a single pair of the upper tool 11 and the lower die 13 are fitted into the turret holes 7 and 9, respectively. In more detail, an up and down movable punch guide 15 (which constitutes a part of the upper tool 11) is located in the turret hole 7. A stripper plate 17 is fixed to the lower end of the punch guide 15 with the help of a straight pin 19 and at least a bolt 21. An up and down movable punch body 23 is fitted within the punch guide 15. Further, the cutting edge of the punch body 23 is formed with a shear angle 25. The punch body 23 is formed with a key groove 27 into which is engaged a key 29 formed on the upper turret 3 and projecting radially inwardly from the sidewall of the turret hole 7. Above the upper portion of the punch body 23, a cylindrical driver end plate 31 is fixed to a punch driver 33. More precisely, the driver end 31 which projects laterally beyond the punch driver 33 is fixed thereto with a bolt 35, and the punch driver 33 is fixed to the punch body 23 with a bolt 37, passing through the central hole of said punch end plate 31. As shown in Fig. 2, a first damping member 39 made of an elastic material such as urethane or the like having a predetermined deformation or degree range δ is located within an annular space defined by the side face of the punch driver 33, the upper side of the driver end plate 31 and the sides of an annular groove 40 formed in punch guide 15 adjacent to the central hole of the flange portion 15F of said guide 15. Thanks to this particular structure, the first damping member 39 is interposed between the punch guide 15 and driver end 31. As shown in Fig. 2, under normal conditions, that means when the first damping member 39 is not compressed or deformed, the height of said first damping member 39 is equal to the sum of the deformation degree δ and the height of the annular groove 40 formed in the punch guide. Further, the thickness of the annular damping member 39 is such that when, under normal conditions, the inner cylindrical face is in contact with the cylindrical face of the punch driver 33, there remains an annular gap 42 between the outer cylindrical face of the damping member 39 and the opposite cylindrical face of groove 40. This particular feature allows the deformation or deflection of the first annular damping member 39 when the lower face thereof bears against the driver end 31 and its upper face bears against the bottom of groove 40. Further, a guide key 43 is fixed to the driver end 31 with a plurality of bolts 41 and protrudes radially outwards so as to be engaged with the key groove 27. The upper face of the punch driver 33 supports a punch head 45 whereby a second elastically deformable damping member 47 made of a material such as urethane or the like is interposed between an upper face of a flange portion 33F of the punch driver 33 and a lower face of a flange portion of the punch head 45. The height of the second damping member 47 which preferably has an annular cylindrical shape and surrounds a cylindrical portion of the punch head 45 as well as a cylindrical portion of the flange portion 33F of the punch driver 33, is such that in the undeformed condition of said second damping member 47, a gap α exists between the punch driver 33 and the punch head 45. As shown in Figs. 1 and 3, the punch head 45 is fixed to the punch driver 33 with a plurality of bolts 49 passed through imbedding holes 45G formed in the punch head 45 so that the punch head 45 can be moved with respect to punch driver 33 within the limits defined by said gaps α. A stripping spring 51 for urging the punch driver 33 upward is interposed between the upper face of the punch guide 15 and the flange portion 33F of the punch driver 33. Further, a lift spring 53 for urging the punch guide 15 always upward is interposed between the bottom face of a blind annular hole 3H formed in the upper turret 3, and the upper flange portion 15F of the punch guide 15. On the other hand, a die member 55 forming a part of the lower die 13 is fitted to a recess 9 formed in the lower turret 5. This die member 55 comprises a die hole 57 with which the punch body 23 is engaged. Above the punch head 45, an up and down movable striker 59 is mounted on an upper frame (not shown) which constitutes a part of the turret punch press 1. Further, air blow passages 61A, 61B, 61C and 61D are formed in the punch guide 15, the punch body 23 and the bolt 37, respectively in order to discharge chips (produced during punching processing) to the outside thereof. Since, in the embodiment as described above, the deformation or deflection of the first damping member 39 interposed between the punch guide 15 and the driver end 31 is limited within a predetermined deflection or deformation range δ, it is possible to improve the durability of the first damping member 39. In addition, thanks to the provision of a gap α between the punch body 33 and the lower face of the punch head 45, and due to an appropriate height of the second damping member 47, it is possible to limit the deflection or deformation degree of the second damping member 47, so that the durability of the second damping member 47 is also improved. Figs. 4 to 10 show the operation sequence during the punching processing, during which the work W mounted on the lower die 13 is punched by cooperation of the upper tool 11 with the lower die 13. In more detail, Fig. 4 shows the initial state; Fig. 5 shows the state where the striker 59 is lowered to strike the punch head 45 so that a sound A is generated when the striker 59 knocks the punch head 45; Fig. 6 shows the state where the stripper plate 17 and the cutting edge of the punch body 23 both begin to be brought into tight contact with the work W so that a sound B is generated when the stripper plate 17 is applied against the work W and the stripper plate 17 is applied against the die 55; Fig. 7 shows the state where the work W is punched out by the cutting edge of the punch body 23 so that a sound C is generated when the cutting edge of the punch body 23 begins punching the work W; Fig. 8 shows the state where the cutting edge of the punch body 23 shears the work W so that a sound D is generated when the work W is broken off; Fig. 9 shows the state where the punch body 23 is returned upwardly by the urging force of the stripping spring 51 after the work W has been punched so that a sound E is generated by the separation of the cutting edge of the punch body 23 from the work W when returning to its upper position under the action of the stripping spring 51; and Fig. 10 shows the state where the punch body 23 is strongly driven upwardly by the stripping spring 51 so that a sound F is generated when the driver end 31 collides with the punch guide 15. Fig. 11 shows the measured values of the sounds or noises A to F generated during the respective processing stages. Fig. 11 indicates that: sound A is reduced because the second damping member 47 is interposed between the punch driver 33 and the punch head 45; sound B is reduced because a gap α is provided between the punch driver 33 and the punch head 45 and in addition the second damping member 47 is interposed between the punch driver 33 and punch head 45, and the application of the force of the stripping spring 51 is attenuated by the second damping member 47. The sound C can be reduced because the punch body 23 is formed with a shear angle 25, so that the punch body 23 can easily start cutting the work W. The sound D can be also reduced because the punch body 25 is formed with the shear angle 25. Further, since the punching load can be reduced, the deformation of the press frame can be decreased, so that the noise generated by the press body can be also lowered. In the same way, the sound E can be reduced because the punch body 23 is formed with a shear angle 25, so that the resistance opposed by the work W is increased gradually when the cutting edge of the punch body 23 starts to cut the work W without generating an important resistance at any time. Further, the sound F can be reduced because the first damping member 39 is interposed between the punch guide 15 and the driver end 31. As already mentioned above, thanks to the interposition of the first damping member between the punch guide and the punch driver, it is possible to reduce the noise generated by collision between the punch guide and the punch driver, during the upward projection of the punch body by the stripping spring. In addition, since a second damping member is interposed between the punch driver and the punch head and since the cutting edge of the punch body is formed with a shear angle, it is possible to reduce the noise generated due to other remaining noise generating factors during punching processing, thus reducing the overall noise generated during punching processing.

Claims: A punching tool having a punch body (23), a punch driver (33) connected to the punch body (23), a punch head (45) disposed over the punch driver (33) and struck by a striker (59), a punch guide (15) for guiding the punch body (23), a stripper plate (17) disposed under the punch guide, and a stripping spring (51) interposed between the punch guide (15) and an upper portion of the punch driver (33), wherein the punch driver (33) is provided with a driver end (31) fixed to a lower portion of the punch driver (33), wherein the driver end (31) is disposed beneath a flanged region (15F) of the punch guide, which flanged region is positioned between the upper portion and the lower portion of the punch driver (33), characterised in that a first damping member (39) is interposed between the flanged region (15F) of the punch guide (15) and the driver end (31) of the punch driver (33) so as to be elastically deformable within a predetermined degree of deflection or deformation, and the stripping spring being disposed between the flanged region (15F) and the upper portion of the punch guide (33). A punching tool as claimed in claim 1, in which a lower portion of the flanged region (15F) has an annular recess (40) which accommodates the first damping member (39). A punching tool as claimed in claim 2 in which the first damping member (39) has a depth greater than the depth of the recess (40) by an amount (δ) which represents the predetermined value or degree of deflection or deformation. A punching tool as claimed in claim 3, in which the first damping member (39) has a width less than the width of the recess (40). A punching tool as claimed in any preceding claim, further comprising a second elastically deformable damping member (47) interposed between the upper portion of the punch driver (33) and the punch head (45). A punching tool as claimed in claim 5, in which the second elastically deformable damping member (47) allows movement of the punch driver (33) relative to the punch head (45) within a predetermined degree corresponding to deformation of the second damping member (47). A punching tool as claimed in any preceding claim, wherein a cutting edge of the punch body (23) is formed with a shear angle (25).

Inventors: FUJITA ORIYA, FUJITA, ORIYA
Applicants: AMADA METRECS CO, AMADA METRECS COMPANY, LIMITED
Application year: 1994
Main classification: B21D45
IPC codes: B30B15, B21D45, B21D28